Theoretical Insights into the Selective Extraction of Americium(III) over Europium(III) with Dithioamide-Based Ligands

Cui Wang; Qun-Yan Wu; Xiang-He Kong; Cong-Zhi Wang; Jian-Hui Lan; Chang-Ming Nie; Zhi-Fang Chai; Wei-Qun Shi

doi:10.1021/acs.inorgchem.9b01200

Theoretical Insights into the Selective Extraction of Americium(III) over Europium(III) with Dithioamide-Based Ligands

Inorg Chem. 2019 Aug 5;58(15):10047-10056. doi: 10.1021/acs.inorgchem.9b01200. Epub 2019 Jul 9.

Authors

Cui Wang^{1

2}, Qun-Yan Wu¹, Xiang-He Kong^{1

2}, Cong-Zhi Wang¹, Jian-Hui Lan¹, Chang-Ming Nie², Zhi-Fang Chai^{1

3}, Wei-Qun Shi¹

Affiliations

¹ Laboratory of Nuclear Energy Chemistry , Institute of High Energy Physics, Chinese Academy of Sciences , Beijing 100049 , China.
² School of Chemistry and Chemical Engineering , University of South China , Hengyang 421001 , China.
³ Engineering Laboratory of Advanced Energy Materials , Ningbo Institute of Industrial Technology, Chinese Academy of Sciences , Ningbo , Zhejiang 315201 , China.

PMID: 31287677
DOI: 10.1021/acs.inorgchem.9b01200

Abstract

Separation of trivalent actinides An(III) from lanthanides Ln(III) is a worldwide challenge owing to their very similar chemical behaviors. It is highly desirable to understand the nature of selectivity for the An(III)/Ln(III) separation with various ligands through theoretical calculations because of their radiotoxicity and experimental difficulties. In this work, we have investigated three dithioamide-based ligands and their extraction behaviors with Am(III) and Eu(III) ions using the scalar-relativistic density functional theory. The results show that the dithioamide-based ligands have stronger electron donating ability than do the corresponding diamide-based ones. All analyses including geometry, Mulliken population, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbital) suggest that the Am-S/N bonds possess more covalency compared to the Eu-S/N bonds, and the M-S bonds have more covalent character than the M-N bonds. Thermodynamic results reveal that N²,N⁹-diethyl-N²,N⁹-di-p-tolyl-1,10-phenanthroline-2,9-bis(carbothioamide) (L¹) has a stronger complexing ability with metal ions owing to its rigid structure and that N⁶,N^6'-diethyl-N⁶,N^6'-di-p-tolyl-[2,2'-bipyridine]-6,6'-bis(carbothioamide) (L²) shows a higher selectivity for the Am(III)/Eu(III) separation. In addition, these dithioamide-based ligands possess Am(III)/Eu(III) selectivity higher than those of the corresponding diamide-based ones, although the former have weaker complexing ability with metal ions, probably due to the greater covalency of the M-S bonds. This theoretical evaluation provides valuable insights into the nature of the selectivity for the Am(III)/Eu(III) separation and information on designing of efficient An(III)/Ln(III) separation with dithioamide-based ligands.